Late Cretaceous-Eocene exhumation of the northern Lhasa terrane and topographic implications for the Central Tibet

Abstract

The central Tibetan Plateau has an average altitude of ∼5000 m; its exhumation and chemical weathering greatly influence the global climate and ocean chemistry. The modern central Tibet is characterized by low-relief, high elevation topography with endorheic drainage. When and how these geomorphic characteristics of central Tibet were initiated remains controversial. Here, we have applied zircon UPb dating and low-temperature thermochronology on the Cretaceous plutons from Coqin Basin of central Tibet in order to assess timings of exhumation. The thermal history modeling indicates a period of relatively rapid cooling (2.5–4 °C/Ma) occurred in Late Cretaceous to Middle Eocene times (from ∼80 Ma to ∼40 Ma), with the exhumation rates of 0.2–0.4 mm/yr assuming a geothermal gradient of 25 °C/km. Cooling rates then slowed to ∼0.5 °C/Ma during the Middle Eocene to the present, with a relatively lower exhumation rates of ∼0.02–0.03 mm/yr. Synchronous rapid cooling and exhumation has also been identified in central Tibet; this signal of widespread Late Cretaceous exhumation across the region may be viewed as evidence for the initial surface uplift and erosion of the central Tibetan plateau. Lower exhumation rate since ∼40 Ma, combined with sedimentological data suggests that the low-relief, internally drained topography of central Tibet was initiated around this time.